Pour dark rum, coconut rum, pineapple juice, orange juice, lime juice and grenadine in a shaker with ice. Cover and shake vigorously. Strain into a glass with ice.
Garnish with sliced pineapple, sliced orange and/or maraschino cherry, if desired.
Notes
This recipe yields 10 ½ ounces, enough for 1 large glass or 2 smaller glasses.
To make by the pitcher - pour dark rum, coconut rum, pineapple juice, orange juice, lime juice and grenadine into a pitcher. Stir to combine and pour into glasses with ice.